The specific aims of this work are: 1. to pruify several HL-A antigens from cultured human lymphocyte cell lines, using both papain and detergent solubilization; 2. to carry out structural studies on purified HL-A antigens in order to examine the question of the nature of the specific immunological determinant in each; 3. to sequence the heavy chain of several HL-A antigens in order to determine the extent of sequence homology to human immunoglobulins; 4. to study the cleavage of the detergent solubilized HL-A antigens by papain and to study the nature of the fragments released by papain in order to study the nature of the insertion of these molecules into the lymphocyte membrane; 5. to study the nature of other products of the major histocompatibility complex in man (Ia antigens), some of which appear to be co-purified with HL-A antigens; 6. to study aspects of pathology relating to HL-A antigens, notably the linkage between HL-A27 and susceptibility to several autoimmune diseases; and the high linkage between the Singapore-2 allele and susceptibility to nasopharyngeal carcinoma; 7. to study functions of HL-A antigens, possibly in cell-cell interactions in the immune response and in differentiation.